In oil and gas wells with highly corrosive environments, it is sometimes desirable to inject chemical inhibitors into the producing stream to prevent damage to the well tubing. A conventional chemical injection valve is operated by a bellows enclosing a gas pressure charge, such as the Type BKLK-2, sold by Camco, Incorporated. Conventionally, the chemical injection valve is positioned in a sidepocket mandrel such as a Camco Type K mandrel in a well bore and is typically used for either a continuous flow or an intermittent chemical injection into the well. The valve is operated in response to a surface chemical pressure pump through a separate control conduit or the annulus around the well tubing to open the injection valve and allow injection of chemicals into the well. Such an application is more fully described and shown on page 11 of the Camco Condensed Catalog 82/83 which is incorporated herein by reference.
As wells are completed at greater depths, higher pressures (for example 10,000 psi) and temperatures are encountered and conventional bellows actuated valves are not satisfactory. That is, chemical injection valves frequently are required to open and close as many as 200,000 times in service and a bellows that is designed to provide the layers of metal of convoluted high strength to withstand high pressures will create a high spring rate effect and overstress, which will result in fatigue and failure.
The present invention is directed to providing an actuating piston to replace the bellows which will withstand the higher pressure and temperatures encountered and once opening pressure is achieved, travel in the piston valve may continue to assure full opening for maximum flow rate at injection. The piston actuated valve accomplishes this function with a lack of increasing forces such as spring or bellows rate. The volume of compressed gas is maximized in the piston actuated valve to prevent minimal charge pressure increase due to valve stem travel.